Spa shell



FIG. 1 is a perspective view of a spa shell, showing our new design;

FIG. 2 is a top view thereof;

FIG. 3 is a front view thereof, the rear view being identical thereto; and,

FIG. 4 is a side view thereof.

The broken line showing is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a spa shell, as shown and described. 